The invention relates to improved properties of synthetic spun fibers and especially to the mechanical (strength-elongation) properties, the texturability by means of friction units or gas jet turbulence and the subsequent treatability without the interpolation of a separate stretching operation.
Synthetic fibers have been known for a long time and are mass produced. They are produced as synthetic yarn from polymers such as polyester, polyamide 6 or polyamide 66.
The synthetic fibers manufactured from these polymers have, in general, a very low orientation level, low strengths and high elongations at break, as well as inadequate thermal stability. For use in textile finishing of acceptable quality, the synthetic fibers are subjected to a separate stretching process (split process). This process is bothersome; it requires the winding up of the yarns after each operation.
In order to decrease the number of separate operations, integrated fiber stretching processes are also known (Chantry, et al, U.S. Pat. No. 3,216,187). The spun thread is stretched several times its length, without intermediate winding up, directly between rotating godet wheels. This process produces yarns of high strength and low elongations at break, comparable with the yarns from a split process.
In McNamara, et al, U.S. Pat. No. 4,123,492, polyamide 66 yarns are subjected, immediately after the spinning, under definite tension conditions, to a temperature treatment. The tensions are set by means of air turbine-driven rolls running at different speeds. The yarns produced in this way are practically ready-stretched with low elongations at break and specified values of the initial modulus, the 10% modulus and the final modulus.
The additional units required in the fiber stretching complicate the spinning process and finally reach technical limits (stability, temperature constancy) at very high speeds.
In recent times, synthetic fibers have been produced at high draw-off speeds, especially between 2,700 and 4,000 m/min, characterized by a certain degree of pre-orientation (partially oriented yarn/POY). These yarns are particularly suitable for further treatment in a stretch texturing process.
From Plazza et al., U.S. Pat. No. 3,772,872 and Petrille, U.S. Pat. No. 3,771,307, specifications for polyester POY raw yarns are already known which are said to be suitable for "false twist" texturing under special conditions. Noticeable are spinning speeds of .gtoreq.2,750 m/min, a birefringence of .gtoreq.0.025, elongations at break between 70 and 180% or a boiling shrinkage of 40-60%. The patents give no indication of the friction texturing or the blowing turbulence. The spindle texturing procedures given therein differ in their mode of operation (friction behavior, tensions before and after the spindle) basically from the mentioned newer processes, which are carried out at considerably higher texturing speeds.
Because of the elongation limitation to .gtoreq.70% or the boiling shrinkage between 40-60%, these synthetic fibers are not usable for direct textile applications. Under mechanical and thermal stress the finished fabric is not stable. It is under these circumstances that the present invention was conceived.